This invention relates to a magnetic head in which the area around the gap is formed of a thin ferromagnetic metal film, as well as a process for producing said magnetic head. More particularly, the invention relates to a magnetic head characterized by improved corrosion resistance of the thin ferromagnetic metal film.
With a view to providing improved saturated flux density in levitation and other types of magnetic heads, a structure called the metal-in-gap type has heretofore been adopted and this structure is characterized by the attachment of a thin film of a ferromagnetic metal such as Sendust to the gap forming face of a substrate (core) which is formed of a magnetic oxide (e.g., ferrite) or a nonmagnetic oxide. A problem with this approach is that if a thin ferromagnetic metal film is formed on the ferrite by a deposition technique such as sputtering, an undesirably modified layer forms between the oxide in the core and the thin ferromagnetic metal film, causing deterioration in characteristics such as increased magnetic resistance or impaired soft magnetic properties and, what is more, the modified layer may occasionally serve as a pseudo-gap. Another problem with the thin ferromagnetic metal film is that it can potentially cause corrosion during cutting, cleaning and other steps of the fabrication process.
With a view to solving these problems of undesirable modification and corrosion, it has been proposed that a magnetic head of the type shown in FIG. 1A (cross-sectional side view) and FIG. 1B (plan view) in which one of the opposing surfaces of ferrite or otherwise formed substrates 1 and 2 is provided with a thin ferromagnetic metal film 3, with an SiO.sub.2 or otherwise formed gap member 4 being inserted between the thin ferromagnetic metal film 3 and the substrate 2 and bonded by means of glass 5 should have a film 6 of nonmagnetic metal such as Cr, Ti or Si that is provided between the thin ferromagnetic metal film 3 and each of the substrates 1 and 2. Alternatively, it has been proposed that a magnetic head of the type shown in FIG. 2A (cross-sectional side view) and FIG. 2B (plan view) in which the thin ferromagnetic metal film 3 is formed on the two opposing surfaces of the substrates 1 and 2 should have a film 6 of nonmagnetic metal such as Cr, Ti or Si that is provided not only between the thin ferromagnetic metal film 3 and each of the substrates 1 and 2 but also between the gap member 4 and each thin ferromagnetic metal film 3. (See Unexamined Published Japanese Patent Application (kokai) Sho 61-172203 or Unexamined Published Japanese Patent Application (kokai) Hei 4-241205) The basic idea behind the provision of the nonmagnetic metal film 6 in those prior art magnetic heads is to insure that the nonmagnetic metal element will not diffuse so much into the thin ferromagnetic metal film 3 as to widen the pseudo-gap between the magnetic layers and, hence, glass of a low-melting point of about 350.degree. to 450.degree. C. is employed to prevent diffusion of that element during fusion of the substrates 1 and 2 by means of glass 5.
However, these conventional magnetic heads have had the problem that it is not always possible to insure satisfactory corrosion resistance for the thin ferromagnetic metal film 3.
Stated more specifically, the recent trend in magnetic recording and reproduction to increase the density of recording signals on a magnetic recording/reproducing apparatus has made it necessary that the ferromagnetic film for use in the magnetic head be formed of a material having a higher saturation flux density Bs. Ferromagnetic films for use in magnetic heads are generally made of FeAlSi (Sendust alloys) and NiFe (permalloys) which have saturation flux densities (Bs) on the order of 1 T. Candidates under review for materials having higher saturation flux densities are Fe base microcrystalline films typified by those of Fe--M--N and Fe--M--C (M=Zr, Ta, Nb, Hf, etc.) which have saturation flux densities (Bs) in excess of 1.5 T. However, these materials have the drawback that they contain more Fe than Sendust alloys and permalloys and, hence, are poor in corrosion resistance.
In order to improve the corrosion resistance of the thin ferromagnetic metal film 3, it has been proposed that the formation of the nonmagnetic metal film 6 be replaced by the addition of certain elements to said thin metal film 3. Take, for example, Sendust alloys as ferromagnetic metals; addition elements that are effective include elements of group IVa (Ti, Zr and Hf), elements of group Va (V, Nb and Ta), elements of the platinum group (Ru, Rh, Pd, Os, Ir and Pt), Cr, etc. On the other hand, Cr, Al, Si, etc., have been found to be effective for the Fe-base microcrystalline films.
To add these elements to the thin ferromagnetic metal films, sputtering may be performed using an alloy or composite target that has a predetermined element already added thereto in a predetermined amount. However, the addition of these elements by sputtering will cause segregation and it is difficult to have them distributed uniformly in the thin ferromagnetic metal film. As a result, one often fails to assure the desired corrosion resistance and the production yield is low. If, on the other hand, the addition of those elements is increased with care being taken to prevent segregation while insuring to provide a practical level of corrosion resistance, deterioration in characteristics occurs in one way or another, as exemplified by significant decrease in the saturation flux density Bs of the thin ferromagnetic metal film 3 or the failure to provide high permeability. Thus, it has been difficult to provide improved corrosion resistance while maintaining satisfactory magnetic characteristics.
A further problem concerns adhesion strength and the ferromagnetic film has often separated from the oxide substrate during a machining step such as a cutting operation.